(1) Field of the Invention
The present invention relates to a novel tape cassette for use in magnetic recording/reproducing apparatus of fixed head type. More specifically, the present invention is directed to provide a tape cassette having magnetic tape and a pressure pad incorporated therein, and in particular suitable for positioning the pressure pad precisely relative to the magnetic head. The present invention is effective for a tape cassette used for a magnetic recording/reproducing apparatus of fixed head type which performs recording operations using a large number of tracks at a high recording frequency.
(2) Description of the Prior Art
FIG. 1 shows a embodiment of an prior art tape cassette. An illustrated tape cassette 1 indicates a compact type cassette, which has magnetic tape 2 and a pressure pad 3 incorporated therein. The pressure pad 3 is adhesively supported by a pad base 4. The pad base 4 with the pressure pad 3 is supported by pad base supporting pins 6a, 6b and 7a, 7b, all of which are integrally resin-molded as part of a cassette half 5b. Next referring to FIG. 2, once a magnetic head 8 is inserted in the tape cassette 1, the magnetic tape 2 is pressed against the magnetic head 8 by the pressure pad 3 with a constant pressure. In this state, with the magnetic tape 2 running, the magnetic head conducts recording or reproducing operation of signals. In this situation, the pressure of the pressure pad 3 is mainly generated by deformation or curvature of the pad base 4. This pressing force by the pressure pad 3 determines a space between the magnetic head 8 and the magnetic tape 2. The space has an intimate relation with the recording frequency, that is, if the recording frequency is high, the space need be set narrow.
Meanwhile, in order to effect recording/reproducing operations with stability, it is necessary that the pressure pad 3 presses the magnetic tape 2 against the magnetic head 8 with a uniform pressure distribution. Particularly, the pressure distribution across the width direction of the magnetic tape 2, or along the direction across which a large number of recording/reproducing tracks are disposed in parallel with one another, has a great influence on recording/reproducing characteristics in each track, therefore, control with high precision is desired. In other words, the alignment or the degree of parallelism between a facing surface 3a of the pressure pad 3 to the magnetic head 8 and a facing surface 8a of the magnetic head 8 to the pressure pad 3 can pose a problem. In the prior art tape cassette 1, since the pressure pad 3 is held adhesively, as stated above, by the pad base 4, the pad base 4 in practice should be supported in parallel with the facing surface 8a. Here, it is possible to arrange the facing surface 3a relative to positioning support surfaces 4a, 4b (to be abbreviated simply as supporting surfaces 4a, 4b hereinafter) in a degree of parallelism which would not cause a problem.
The pad base 4 is supported by the pad base supporting pins 6a, 6b, 7a and 7b as stated above. More specifically, when the magnetic head 8 is not inserted in the tape cassette 1, the pad base 4 is supported movable in a direction of the magnetic head 8 insertion with constant clearances provided between pad base supporting pins between 6a and 7a, and between 6b and 7b. On the other hand, when the magnetic head 8 is inserted in the tape cassette 1, the pad base 4 is pressed and supported with the supporting surfaces 4a and 4b abutting against the pad base supporting pins 6a and 6b, respectively. Accordingly, to sum up for general analysis, the pressure distribution of the magnetic tape 2, is dependent upon the parallelism of the facing surface 8a of the magnetic head 8 relative to the pad base supporting pins 6a and 6b. Here, as concern the pad base supporting pins 6a and 6b, since these pad base supporting pins 6a and 6b are integrally resin-molded as part of the cassette half 5b as mentioned above, the pins are provided with draft for molding die, so that the shape of the pins is tapered in place of uniform cylindrical form. As a result, it is very difficult to control the parallelism of the pins to the facing surface 8a with high accuracy.
In the prior art, to overcome this problem, the torsional rigidity of the pad base 4 across the width of the magnetic tape 2 is optimized such that the deviation of parallelism between the facing surfaces 8a and 3a can be absorbed by the twisting of the pad base 4. This, however, could not be a drastic measure for uniformalizing the aforesaid pressure distribution, and thus the problem has been an obstacle to performing high recording density.
It is also desirable to control the absolute value of the pressing force generated by the pressure pad 3 itself so as not to deviate from a set-up value. Basically, the pressing force is determined by the positional relationship between the magnetic head 8, the pressure pad 3 and the pad base 4, if a spring constant of the pad base 4 with respect to the head inserting direction is fixed. Here, the pressure pad 3 and the pad base 4 are formed integrated, therefore if the tolerance of the thickness of the pressure pad 3 is neglected, the positional relationship between the magnetic head 8 and the pad base 4 is a matter to be considered. If the magnetic head 8 is inserted in the tape cassette 1, the position of the magnetic head 8 is regulated with high precision on the mechanism of a tape recorder or the like. On the other hand, the pad base 4 is positioned such that the support surfaces 4a and 4b abut against the pad base supporting pins 6a and 6b, that is, the position of the pad base 4 is dependent upon the bad base supporting pins 6a and 6b. As stated above, the pad base supporting pins 6a and 6b are resin-moulded integrally with the cassette half 5b, which in turn is positioned relative to the above-said mechanism by reference holes 9a and 9b receiving unillustrated reference pins (for positioning the cassette half 5b) planted on the mechanism.
To summarize what has been discussed above, the positioning accuracy of the pad base 4 to the magnetic head 8 is determined by the sum of the following four elements:
(A) an assembling tolerance at the time when the magnetic head 8 is assembled to the mechanism (namely, the dimensional tolerance of the distance between the magnetic head 8 and the reference pins on the mechanism); PA1 (B) a positioning tolerance at the time when the cassette half 5b (or the tape cassette 1 in a broad sense) is fitted in the mechanism; PA1 (C) a positional tolerance of the distance between the reference holes 9a and 9b on the cassette half 5b and the pad base supporting pins 6a and 6b; and PA1 (D) a thickness tolerance of the pressure pad 3.
Of these, the item (C) is dependent upon the molding accuracy of the cassette half, and the accuracy of this has been particularly difficult to regulate.
Various kinds of proposals have been disclosed as regards the present invention. Namely, Japanese Utility Model Laid-Open Publication No.sho-60-140276/1985 discloses a tape cartridge (corresponding to the tape cassette) including a spring plate for supporting a pad disposed with both ends thereof abutted against the inner part of a front opening of the body case, characterized in that both ends of the spring plate are supported through elastic cushion means by spring receiving means disposed on the body case. The tape cartridge, according to the disclosed publication, is arranged such that both ends of the spring plate (corresponding to the pad base) are supported by the spring receiving means (corresponding to the pad base supporting pins) on the side of the body case through cushion means. This arrangement can prevent a defective assembled posture of the spring plate and the positional displacement in operation. The method of the disclosure can compensate for the molding tolerance of the pad base supporting pins in some degree, but is not enough to regulate the parallelism of the pad base in high precision, or the above element (C) could not be eliminated.
Another proposal is made by Japanese Utility Model Publication Laid-Open No.sho-63-58387/1988, which discloses a tape cartridge having a pad means comprising a pair of tape guiding pins planted right and left inside a window disposed on the front side of a body case for receiving a magnetic head; a pair of pad supporting ribs disposed on the right and left, and in an inner side of, the tape guide pins; a plate spring with both ends thereof bent backward to form bending pieces; and a pad provided on the front side of the plate spring. The pad means is abutted to and supported by the pad supporting ribs at intermediate portions between the pad on the plate spring and each of the bending pieces. The tape cartridge disclosed by the publication is characterized in that the pad supporting ribs for supporting the pad means (corresponding to the pad base) in its width direction, are disposed closer to the pad than the tape guide pins, so that the pad means may be supported upright on the supporting ribs. In the method of this publication, the parallelism of the pad means is affected greatly by the molding accuracy of the supporting ribs, therefore the difficulty in accuracy control cannot be eliminated.